Pivoted blade assemblies for rotary mowers

ABSTRACT

A blade holder, for a rotary scythe-type lawnmower, whcih is constructed as a circular plate formed as an upright truncated cone with a flat top and a flanged base, and wherein a diametral portion is depressed across the cone and has a medial part for mounting of the blade holder to a drive shaft from the lawnmower, and end portions containing mounts for pivotable cutting blades.

United States Patent Meyer et al. 1 1 Sept. 4, 1973 PIVOTED BLADEASSEMBLIES FOR [56] References Cited ROTARY MOWERS UNITED STATES PATENTS[75] Inventors: Dolph Allan Meyer, Turramurra; 3,203,161 8/1965 Breischet a1. 56/295 Edward Henry Sykes, Greenacre, 3,540,198 11/1970 Heth etal. 56/295 New South Wales, both of Australia Assignee: Victa Limited,Milperra, New South Wales, Australia Filed: Sept. 26, 1972 Appl. No.:292,357

Primary Examiner-Louis G. Mancene Att0rneyS. Delvalle Goldsmith et al.

[57] ABSTRACT A blade holder, for a rotary scythe-type lawnmower, whichis constructed as a circular plate formed as an upright truncated conewith a flat top and a flanged base, and wherein a diametral portion isdepressed across the cone and has a medial part for mounting of theblade holder to a drive shaft from the lawnmower, and end portionscontaining mounts for pivotable cut- Foreign Application Priority DataSept. 28, 1971 Australia 6459 U.S. Cl. 56/295 Int. Cl A0ld 55/18 1 Fieldof Search 56/295 b 8 Claims, 8 Drawing Figures I 18 n r o r PATENTED E 4SHEET 1 [1F 3 PATENTEUSEP 4191s I 3755999 SHEET 2 [1F 3 PIVOTED BLADEASSEMBLIES FOR ROTARY MOWERS This invention relates to the assembliesutilized in rotary scythe-type lawnmowers which incorporate cuttingblades rotatably mounted upon a blade holder which in turn is bolted tothe end of the drive shaft from the lawnmower power unit.

In the use of such assemblies many earlier attempts have been made toovercome undesirable effects upon these assemblies resulting from thestraightening action of centrifugal forces generated by their rotationduring operation of the lawnmower. An important requirement is that thecutting edges of the blades operate in a plane beneath the remainder ofthe assembly in order, among other things, to avoid wear and damagethereto by contact with the grass and ground. As a means of achievingthis requirement cutting blades have either been downwardly stepped ordownwardly inclined from their mounts towards their cutting edges whilethe blade holders have been produced of upright conical form with thedrive shaft connected to the apex thereof.

However, due to the fast rate of rotation of these assemblies theseprovisions have not been entirely satisfactory due to the centrifugalforces straightening and flattening effect both on the blades as well ason the conical shape of the blade holders. Furthermore, the flexing andrelaxing of the assembly from changes in these forces resulting fromalteration in the speed of the power unit, particularly when thelawnmower is stationary, has resulted in excessive depth of cut of thegrass in places, even to the point of scorching of the grass roots.

It is the principal object of this invention to provide a blade mountingassembly which at least partially avoids these defects.

In one general form the invention provides a cutting blade mountingassembly for fixture on a drive shaft of a rotary scythe-type lawnmower,comprising a circular blade holder of inverted dish-shape having anupright conical body wall connecting a medial flat-topped portion withthe periphery of the circular blade holder, a diametral depressedportion extending across the blade holder, and having a medial partdepressed from said flat-topped portion and providing means for fixtureto said drive shaft, and mounting means on opposite end sections of thediametral depressed portion providing rotatable mounting for respectivecutting blades.

The invention will now be described with reference to two preferredembodiments shown by the accompanying drawings in which:

FIG. 1 is a plan view of a first form of blade holder with itsassociated blade secured thereto;

FIG. 2 is an enlarged fragmentary side view in section of the bladeholder shown in FIG. 1 with the associated blade displaced from itsmounting position;

FIG. 3 is an end elevation of the blade shown in FIGS. 1 and 2;

FIG. 4 is a plan view of a second form of blade holder;

FIG. 5 is a side elevation of the blade holder shown in FIG. 4;

FIG. 6 is an enlarged fragmentary side view in section of the bladeholder shown in FIGS. 4 and 5 with a second form of blade displaced fromits mounting position;

FIG. 7 is a plan view of the blade shown in FIG. 6; and,

FIG. 8 is an end elevation of the blade shown in FIGS. 6 and 7.

With reference to FIGS. 1 to 3 a blade holder 9 of inverted dish-shapedform has an upright conical body wall 9A with a flattened plateau 10 atits peak. The base of the conical wall 9A is bent upwardly at 13 to forma peripheral upright flange 13A for reinforcement of the periphery ofthe blade holder 9. The underside of the bend 13 is in the same planethroughout the periphery of the blade holder. Diametrally across theupper face of the blade holder 9 a substantially rectangular beam-likeportion 20 of the conical blade holder 9 is depressed to provide acentral substantially flat mounting platform 20A apertured to accept thelower end (not shown) of the drive shaft of a power unit for thelawnmower and which is at a level beneath that of the plateau 10.Preferably, the material of the blade holder 9 is stepped downwardly at16 from the conical wall 9A at an inclined angle to avoid weakeningrightangular bends. The depressed portion 20 to either side of theplatform 20A is inclined somewhat less than the angle of inclination ofthe conical wall 9A whereby opposite terminal ends 208 of the portion 20extend radially for a distance to join the bend 13 and to be coplanarwith its underside. An upward circular impression 21 is formed in eachterminal end 208. A multi-sided mounting hole 18 for a cutting blade isprovided in each impression 21.

In the design of a blade holder 9 of the above type the spacing betweenthe planes of the terminal ends 208 and the platform 20A of the portion20 will conform to the requirements normally attendant a blade holderfor a specific lawnmower dependent to a large extent upon the length ofthe drive shaft. I-Iitherto the conical angle of the wall of the dishedholder has been dictated by the spacing of the above mentioned planes.By this invention the conical angle of most of the wall of the bladeholder 9 is increased considerably from that which would be normallypossible, with corresponding greater resistance to flattening of thecone as the result of centrifugal forces.

The embodiment shown by FIGS. 1 to 3 is intended to be used with acutting blade 11 which is substantially flat and slightly twisted as at12 to improve cutting and to reduce grass drag. This blade does not havean upswept trailing edge as it is of the kind designed for use without agrass catcher on the lawnmower, and, therefore, requiring less airturbulence beneath the baseplate. The blade 11 will often rotate on itsmount during operation whether or not it strikes an obstruction, thusconforming with the normal functioning of cutting blades, and ispermitted to foul slightly the bend 13. It is, however, permitted toretract from the path of the obstruction to reduce its impact therewith.This will avoid the danger of creating a hazard of high velocityprojectiles. The blade 11 at its root end portion is upwardly impressedto fonn a mounting contour 22 for accommodation within the impression21. The head of the bolt 14, will, in turn, be accommodated within thecontour 22 and will be shielded from wear by the body of the blade 11.The peripheral bend 13 on the blade holder 9 will bear upon the uppersurface of the blade I l to support it against flexing and lifting fromcentrifu gal force. As explained above, the increased conical angle ofthe wall 9A which extends over almost all of the body of the bladeholder 9 also functions to resist elevation of the bend l3, andconsequently the blade, even in conditions of extreme centrifugalforces.

The embodiment shown in FIGS. 4 to 8 incorporates a similar diametral,rectangular beam-like portion 20 depressed from a conical wall 15 andconnected therewith by an inclined step 17. An impression 21 is providedin each terminal end 208 of the diametral portion 20 to receive themounting contour 22 of a cutting blade 19 of a kind suitable for usewith lawnmowers incorporating grasscatchers. The blade 19, for thispurpose, is provided with an upswept trailing edge portion 23 on a bodythat is substantially flat for mounting in a horizontal plane. Asrevealed in FlGS. 6 and 8 the outer end portion of the blade 19 istwisted slightly to provide a downward step 24 from its leading edge andextending part way across the blade so that the leading edge near itsouter extremity is provided with a cutting edge 25 beneath the level ofthe body of the blade 19. A cutting blade constructed in this way has acentre of gravity approximately in the same plane as the bend l3 andconsequently will not flex to any marked degree under the influence ofcentrifugal forces. Furthermore, due to the above described constructionof the blade holder 9 the plane of the bend 13 itself will not rise toany marked degree under centrifugal forces and thus a blade cuttingassembly results which is substantially rigid under operating conditionswithout the requirement for the use of heavier gauge metal or otherprovisions which would lead to a substantial increase in the weight ofthe assembly.

However, where cutting blades of this latter type are employed theupswept edge 23 would foul the bend l3 and flange 13A of the bladeholder 9, shown in FIGS. 1 and 2, and prevent the blade 19 fromretracting upon impact with an obstruction on the lawn, therebyresulting in the danger of creating a projectile ejected from beneaththe lawnmower. To avoid this effect the peripheral edge of the bladeholder defined by the bend 13 is upwardly curved or arched to eitherside of each terminal end 208 of the diametral portion to provide aclearance passageway 26 beneath the peripheral edge for the upswept edge23 of the blade 19 to pass in a full circle about its securing mount inthe impression 21. The conical wall 15A of the blade holder 15 is formedto blend to the curved peripheral edge to complete the passageway 26. Asa result the blade 19 will completely retract upon striking an obstacle,or during fluctuation in rotating speed of the blade holder 15, thuslargely avoiding creation of the above mentioned hazard to bystanders,as well as avoiding wear and damage by impact of the upswept edge 23with the periphery of the blade holder 15.

Two exemplary forms of pivotted blade assemblies for lawnmowers havebeen described in the foregoing passages but it is to be understood thatother forms as well as modifications thereto are feasible within thescope of this invention. It should beunderstood that throughout thisspecification where terms such as depressed," upright," upper andunderside are used which relate to the disposition of the equipment, itis to be assumed that the equipment is located in its normal operatingposition.

What we claim is:

1. A cutting blade mounting assembly for fixture on a drive shaft of arotary scythe-type lawnmower, comprising a circular blade holder ofinverted dish-shape having an upright conical body wall connecting amedial flat-topped portion with the periphery of the circular bladeholder, a diametral depressed portion extending across the blade holder,and having a medial part depressed from said flat-topped portion andproviding means for fixture to said drive shaft, and mounting means onopposite end sections of the diametral depressed portion providingrotatable mounting for respective cutting blades.

2. An assembly according to claim 1, wherein the mounting means for eachcutting blade is an underside circular recess formed as an impression inan end section of the diametral depressed portion.

3. An assembly according to claim 2, wherein a corresponding circularimpression is provided in the mounting end of the cutting blade forrotatable accommodation within the circular recess, a fixing bolt forthe cutting blade passing through the recess and the blade impressionwith its head at least partly concealed within the blade impression.

4. An assembly according to claim 1, wherein the diametral depressedportion has arms at opposite sides of its said medial part which areinclined downwardly at an angle less than the conical angle of saidconical body wall.

5. An assembly according to claim 1, wherein the cutting blades eachhave an upswept trailing edge, and the periphery of the blade holderadjacent the cutting blade mounting means is archedto permit passage ofthe blade beneath the blade holder.

6. A blade holder for the cutting blades of a rotary scythe-typelawnmower, and fixable to a drive shaft of said lawnmower, comprising acircular plate formed as an upright cone with a flattened top, aperipheral flange formed around the base of the conical plate, adiametral depressed portion in the cone and extending across the conicalplate, and having a medial part depressed from said flattened top andproviding means for fixture to said drive shaft, and opposite endsections on said diametral depressed portion provided with means forrotatably mounting respective cutting blades.

7. An assembly according to claim 6, wherein the diametral depressedportion has arms at opposite sides of its said medial part which areinclined downwardly at an angle less than the conical angle of saidconical body wall.

8. An assembly according to claim 7, wherein the cutting blades eachhave an upswept trailing edge, and the periphery of the blade holderadjacent the cutting blade mounting means is archedto permit passage ofthe blade beneath the blade holder.

* i i i

1. A cutting blade mounting assembly for fixture on a drive shaft of arotary scythe-type lawnmower, comprising a circular blade holder ofinverted dish-shape having an upright conical body wall connecting amedial flat-topped portion with the periphery of the circular bladeholder, a diametral depressed portion extending across the blade holder,and having a medial part depressed from said flat-topped portion andproviding means for fixture to said drive shaft, and mounting means onopposite end sections of the diametral depressed portion providingrotatable mounting for respective cutting blades.
 2. An assemblyaccording to claim 1, wherein the mounting means for each cutting bladeis an underside circular recess formed as an impression in an endsection of the diametral depressed portion.
 3. An assembly according toclaim 2, wherein a corresponding circular impression is provided in themounting end of the cutting blade for rotatable accommodation within thecircular recess, a fixing bolt for the cutting blade passing through therecess and the blade impression with its head at least partly conceAledwithin the blade impression.
 4. An assembly according to claim 1,wherein the diametral depressed portion has arms at opposite sides ofits said medial part which are inclined downwardly at an angle less thanthe conical angle of said conical body wall.
 5. An assembly according toclaim 1, wherein the cutting blades each have an upswept trailing edge,and the periphery of the blade holder adjacent the cutting blademounting means is arched to permit passage of the blade beneath theblade holder.
 6. A blade holder for the cutting blades of a rotaryscythe-type lawnmower, and fixable to a drive shaft of said lawnmower,comprising a circular plate formed as an upright cone with a flattenedtop, a peripheral flange formed around the base of the conical plate, adiametral depressed portion in the cone and extending across the conicalplate, and having a medial part depressed from said flattened top andproviding means for fixture to said drive shaft, and opposite endsections on said diametral depressed portion provided with means forrotatably mounting respective cutting blades.
 7. An assembly accordingto claim 6, wherein the diametral depressed portion has arms at oppositesides of its said medial part which are inclined downwardly at an angleless than the conical angle of said conical body wall.
 8. An assemblyaccording to claim 7, wherein the cutting blades each have an upswepttrailing edge, and the periphery of the blade holder adjacent thecutting blade mounting means is arched to permit passage of the bladebeneath the blade holder.